Method to monitor pressure drop across a selective catalyst reducer for engine and exhaust airflow diagnostics

ABSTRACT

A method to diagnose exhaust system malfunction in an electronically controlled internal combustion engine having an exhaust system and including a Selective Catalyst Reducer (SCR) is disclosed. The method may comprise determining ambient barometric pressure; determining a baseline curve of exhaust flow; and monitoring said exhaust flow rate for changes in exhaust flow rate compared to change of exhaust pressure across the SCR to diagnose exhaust system malfunction.

TECHNICAL FIELD

For proper control and diagnosis of an internal combustion engine after treatment system, it is important to accurately determine the exhaust flow rate. The exhaust flow rate may be determined by the engine control logic, and many ways to determine the exhaust flow rate are shown in the literature. However, it has been a recurring problem to confirm the accuracy of the exhaust flow rate determination made by the engine control logic and diagnostic discrepancies due to issues such as exhaust flow exhaust leaks, sensor malfunctions errors in engine calculated flow rate etc. Such errors affect the accuracy of the determination of engine airflow in general. Airflow issues can affect the efficient operation of the engine.

SUMMARY

In one embodiment, the present invention is directed to a method to diagnose exhaust system malfunction in an electronically controlled internal combustion engine having an exhaust system and including a Selective Catalyst Reducer (SCR) with an inlet and an outlet.

In one embodiment, the method may include determining the ambient barometric pressure; determining a baseline curve of exhaust flow; and monitoring the exhaust flow rate for changes in exhaust flow rate compared to change of exhaust pressure across the SCR to diagnose exhaust system malfunction.

In another embodiment, the baseline exhaust flow rate is determined by determining exhaust flow rate pressure at said SCR inlet and determining a baseline of exhaust flow rate versus change of pressure across the SCR.

In another embodiment, the baseline curve of exhaust flow is determined at a first operating engine cycle and stored in memory for use during said engine life. In another embodiment, the baseline curve of exhaust flow is a predetermined value stored in memory in the electronic controller. A shift of the baseline curve of exhaust flow rate versus change of pressure across the SCR over time is indicative of at least one of an exhaust leak, exhaust flow rate sensor malfunction, exhaust pressure sensor malfunction, or error in engine calculated exhaust flow. In addition, determination of engine airflow rate may be made based upon said baseline curve of exhaust flow. Each exhaust system failure may be stored in the electronic controller memory for retrieval and analysis by an operator.

In another embodiment, the method may include an exhaust system further equipped with a diesel particulate filter (DPF) having an inlet and an outlet. The DPF outlet is in fluid communication with the SCR inlet. The SCR inlet has a pressure sensor to generate data signals to the electronic controller indicative of exhaust flow pressure at the SCR inlet.

In one embodiment, the barometric pressure is the pressure of the exhaust flow at the SCR outlet, and the change of pressure across the SCR is determined by comparing the exhaust flow pressure at said SCR inlet to the ambient barometric pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an electronically controlled internal combustion engine;

FIG. 2 is a schematic representation of baseline curve of exhaust flow through an exhaust system;

FIG. 3 is a schematic representation of a flowchart of one method according to the present invention.

DETAILED DESCRIPTION

FIG. 1 illustrates a vehicle powertrain system 10 in accordance with one non-limiting aspect of the present invention. The system 10 may provide power for driving any number of vehicles, including on-highway trucks, construction equipment, marine vessels, stationary generators, automobiles, trucks, tractor-trailers, boats, recreational vehicle, light and heavy-duty work vehicles, and the like.

The system 10 may be referred to as an internal combustion driven system wherein fuels, such as gasoline and diesel fuels, are burned in a combustion process to provide power, such as with a spark or compression ignition engine 14. The engine 14 may be a diesel engine that includes a number of cylinders 18 into which fuel and air are injected for ignition as one skilled in the art will appreciate. The engine 14 may be a multi-cylinder compression ignition internal combustion engine, such as a 4, 6, 8, 12, 16, or 24 cylinder diesel engines, for example. It should be noted, however, that the present invention is not limited to a particular type of engine or fuel.

Exhaust gases generated by the engine 14 during combustion may be emitted through an exhaust system 20. The exhaust system 20 may include any number of features, including an exhaust manifold and passageways to deliver the emitted exhaust gases to a particulate filter assembly 30, which in the case of diesel engines is commonly referred to as a diesel particulate filter. Optionally, the system 20 may include a turbocharger proximate the exhaust manifold for compressing fresh air delivery into the engine 14. The turbocharger, for example, may include a turbine 32 and a compressor 34, such as a variable geometry turbocharger (VGT) and/or a turbo compound power turbine. Of course, the present invention is not limited to exhaust systems having turbochargers or the like.

The particulate filter assembly 30 may be configured to capture particulates associated with the combustion process. In more detail, the particulate filter assembly 30 may include an oxidation catalyst (OC) canister 36, which in includes an OC 38, and a particulate filter canister 42, which includes a particulate filter 44. The canisters 36, 42 may be separate components joined together with a clamp or other feature such that the canisters 36, 42 may be separated for servicing and other operations. Of course, the present invention is not intended to be limited to this exemplary configuration for the particulate filter assembly 30. Rather, the present invention contemplates the particulate filter assembly including more or less of these components and features. In particular, the present invention contemplates the particulate filter assembly 30 including only the particulate filter 44 and not necessarily the OC canister 36 or substrate 38 and that the particulate filter 44 may be located in other portions of the exhaust system 20, such as upstream of the turbine 32.

The OC 38, which for diesel engines is commonly referred to as a diesel oxidation catalyst, may oxidize hydrocarbons and carbon monoxide included within the exhaust gases so as to increase temperatures at the particulate filter 44. The particulate filter 44 may capture particulates included within the exhaust gases, such as carbon, oil particles, ash, and the like, and regenerate the captured particulates if temperatures associated therewith are sufficiently high. In accordance with one non-limiting aspect of the present invention, one object of the particulate filter assembly 30 is to capture harmful carbonaceous particles included in the exhaust gases and to store these contaminates until temperatures at the particulate filter 44 favor oxidation of the captured particulates into a gas that can be discharged to the atmosphere.

The OC and particulate filter canisters 36, 42 may include inlets and outlets having defined cross-sectional areas with expansive portions there between to store the OC 38 and particulate filter 44, respectively. However, the present invention contemplates that the canisters 36, 42 and devices therein may include any number configurations and arrangements for oxidizing emissions and capturing particulates. As such, the present invention is not intended to be limited to any particular configuration for the particulate filter assembly 30.

To facilitate oxidizing the capture particulates, a doser 50 may be included to introduce fuel to the exhaust gases such that the fuel reacts with the OC 38 and combusts to increase temperatures at the particulate filter 44, such as to facilitate regeneration. For example, one non-limiting aspect of the present invention contemplates controlling the amount of fuel injected from the doser as a function of temperatures at the particulate filter 44 and other system parameters, such as air mass flow, EGR temperatures, and the like, so as to control regeneration. However, the present invention also contemplates that fuel may be included within the exhaust gases through other measures, such as by controlling the engine 14 to emit fuel with the exhaust gases.

The exhaust system may also include a Selective Catalyst Reducer (SCR) 11 to introduce a reductant, such as urea or ammonia, either hydrous or anhydrous, to a catalyst bed in the SCR to reduce NOx levels in the exhaust flow stream 23. Generally, the engine may include a NOx engine out sensor 13 and a NOx tail pipe out sensor 15 that are in electronic communication with the electronic controller and transmit data signal indicative of the level of NOx gas in the exhaust. The reductant is stored in a receptacle, such as tank 17, and is introduced into the SCR by at least one reductant injector 19. The reductant injector is in fluid communication 21 with the reductant tank and introduces reductant to the SCR when the received NOx sensor data is indicative of excess NOx levels in the exhaust gas stream.

An air intake system 52 may be included for delivering fresh air from a fresh air inlet 54 through an air passage to an intake manifold for introduction to the engine 14. In addition, the system 52 may include an air cooler or charge air cooler 56 to cool the fresh air after it is compressed by the compressor 34. Optionally, a throttle intake valve 58 may be provided to control the flow of fresh air to the engine 14. Optionally, the throttle intake valve 58 may also be provided to control the flow of EGR gases to the engine 14 or control both fresh air and EGR gases 64 to the engine 14. The throttle valve 58 may be a manually or electrically operated valve, such as one which is responsive to a pedal position of a throttle pedal operated by a driver of the vehicle. There are many variations possible for such an air intake system and the present invention is not intended to be limited to any particular arrangement. Rather, the present invention contemplates any number of features and devices for providing fresh air to the intake manifold and cylinders, including more or less of the foregoing features.

An exhaust gas recirculation (EGR) system 64 may be optionally provided to recycle exhaust gas to the engine 14 for mixture with the fresh air. The EGR system 64 may selectively introduce a metered portion of the exhaust gasses into the engine 14. The EGR system 64, for example, may dilute the incoming air charge and lower peak combustion temperatures to reduce the amount of oxides of nitrogen produced during combustion. The amount of exhaust gas to be recirculated may be controlled by controlling an EGR valve 66 and/or in combination with other features, such as the turbocharger. The EGR valve 66 may be a variable flow valve that is electronically controlled. There are many possible configurations for the controllable EGR valve 66 and embodiments of the present invention are not limited to any particular structure for the EGR valve 66.

The EGR system 64 in one non-limiting aspect of the present invention may include an EGR cooler passage 70, which includes an EGR cooler 72, and an EGR cooler bypass 74. The EGR valve 66 may be provided at the exhaust manifold to meter exhaust gas through one or both of the EGR cooler passage 70 and bypass 74. Of course, the present invention contemplates that the EGR system 64 may include more or less of these features and other features for recycling exhaust gas. Accordingly, the present invention is not intended to be limited to any one EGR system and contemplates the use of other such systems, including more or less of these features, such as an EGR system having only one of the EGR cooler passage or bypass.

A cooling system 80 may be included for cycling the engine 14 by cycling coolant there through. The coolant may be sufficient for fluidly conducting away heat generated by the engine 14, such as through a radiator. The radiator may include a number of fins through which the coolant flows to be cooled by air flow through an engine housing and/or generated by a radiator fan directed thereto as one skilled in the art will appreciated. It is contemplated, however, that the present invention may include more or less of these features in the cooling system 80 and the present invention is not intended to be limited to the exemplary cooling system described above.

The cooling system 80 may operate in conjunction with a heating system 84. The heating system 84 may include a heating core, a heating fan, and a heater valve. The heating core may receive heated coolant fluid from the engine 14 through the heater valve so that the heating fan, which may be electrically controllable by occupants in a passenger area or cab of a vehicle, may blow air warmed by the heating core to the passengers. For example, the heating fan may be controllable at various speeds to control an amount of warmed air blown past the heating core whereby the warmed air may then be distributed through a venting system to the occupants. Optionally, sensors and switches 86 may be included in the passenger area to control the heating demands of the occupants. The switches and sensors may include dial or digital switches for requesting heating and sensors for determining whether the requested heating demand was met. The present invention contemplates that more or less of these features may be included in the heating system and is not intended to be limited to the exemplary heating system described above.

A controller 92, such as an electronic control module or engine control module, may be included in the system 10 to control various operations of the engine 14 and other system or subsystems associated therewith, such as the sensors in the exhaust, EGR, and intake systems. Various sensors may be in electrical communication with the controller via input/output ports 94. The controller 92 may include a microprocessor unit (MPU) 98 in communication with various computer readable storage media via a data and control bus 100. The computer readable storage media may include any of a number of known devices which function as read only memory 102, random access memory 104, and non-volatile random access memory 106. A data, diagnostics, and programming input and output device 108 may also be selectively connected to the controller via a plug to exchange various information therebetween. The device 108 may be used to change values within the computer readable storage media, such as configuration settings, calibration variables, instructions for EGR, intake, and exhaust systems control and others.

The system 10 may include an injection mechanism 114 for controlling fuel and/or air injection for the cylinders 18. The injection mechanism 114 may be controlled by the controller 92 or other controller and comprise any number of features, including features for injecting fuel and/or air into a common-rail cylinder intake and a unit that injects fuel and/or air into each cylinder individually. For example, the injection mechanism 114 may separately and independently control the fuel and/or air injected into each cylinder such that each cylinder may be separately and independently controlled to receive varying amounts of fuel and/or air or no fuel and/or air at all. Of course, the present invention contemplates that the injection mechanism 114 may include more or less of these features and is not intended to be limited to the features described above.

The system 10 may include a valve mechanism 116 for controlling valve timing of the cylinders 18, such as to control air flow into and exhaust flow out of the cylinders 18. The valve mechanism 116 may be controlled by the controller 92 or other controller and comprise any number of features, including features for selectively and independently opening and closing cylinder intake and/or exhaust valves. For example, the valve mechanism 116 may independently control the exhaust valve timing of each cylinder such that the exhaust and/or intake valves may be independently opened and closed at controllable intervals, such as with a compression brake. Of course, the present invention contemplates that the valve mechanism may include more or less of these features and is not intended to be limited to the features described above.

In operation, the controller 92 receives signals from various engine/vehicle sensors and executes control logic embedded in hardware and/or software to control the system 10. The computer readable storage media may, for example, include instructions stored thereon that are executable by the controller 92 to perform methods of controlling all features and sub-systems in the system 10. The program instructions may be executed by the controller in the MPU 98 to control the various systems and subsystems of the engine and/or vehicle through the input/output ports 94. In general, the dashed lines shown in FIG. 1 illustrate the optional sensing and control communication between the controller and the various components in the powertrain system. Furthermore, it is appreciated that any number of sensors and features may be associated with each feature in the system for monitoring and controlling the operation thereof

In one non-limiting aspect of the present invention, the controller 92 may be the DDEC controller available from Detroit Diesel Corporation, Detroit, Mich. Various other features of this controller are described in detail in a number of U.S. patents assigned to Detroit Diesel Corporation. Further, the controller may include any of a number of programming and processing techniques or strategies to control any feature in the system 10. Moreover, the present invention contemplates that the system may include more than one controller, such as separate controllers for controlling system or sub-systems, including an exhaust system controller to control exhaust gas temperatures, mass flow rates, and other features associated therewith. In addition, these controllers may include other controllers besides the DDEC controller described above.

In accordance with one non-limiting aspect of the present invention, the controller 92 or other feature may be configured for permanently storing emission related fault codes in memory that is not accessible to unauthorized service tools. Authorized service tools may be given access by a password and in the event access is given, a log is made of the event as well as whether any changes that are attempted to made to the stored fault codes. It is contemplated that any number of faults may be stored in permanent memory, and that preferably eight such faults are stored in memory.

Turning now to FIG. 2, there is shown a baseline curve of the exhaust flow rate versus the change in pressure across the SCR. The X axis 118 is the exhaust flow rate, and the Y axis 120 is the change in pressure across the SCR. Curve 122 is the nominal baseline curve from a new SCR after treatment system.

The initial baseline curve can be generated via a few different methods. In one embodiment, on a new engine, the curve can be learned on the first driving cycle and the baseline curve so generated will become the baseline curve to which all future comparisons by the method will be made. This “learned” method has an advantage of being learned on a vehicle with all the proper exhaust system in place and is expected to be relatively accurate with respect to part to part and installation of exhaust system variability. However, in order to be completely accurate baseline curve, the system should not have any exhaust leaks, errors in engine airflow determinations, or errors in pressure sensor readings.

In another method, the baseline curve can be calibrated into the electronic controller as a parameter, or a predetermined value. It is expected that the predetermined value or parameter would be done with a representative system and would require calibration to have a good knowledge of the SCR system being utilized in the particular application. This method has an advantage of requiring no on engine learning and does not rely on the system performing perfectly from the factory. For example, if the vehicle was built with an exhaust leak, it would not affect the accuracy of the baseline curve. However, it is also understood that a detailed knowledge is required of the exhaust system being utilized for a given application (i.e., SCR size, design, expected pipe losses, etc., and would not account for any part to part variability or specific pipe configurations.

Regardless of the method utilized to generate the baseline curve, the electronic controller diagnostics will, on a regular basis, create new curves of SCR flow versus change in pressure across the SCR and compare these to the baseline curve. Any shift between these two curves will indicate a malfunction, such as an exhaust leak, sensor malfunction errors in engine airflow determinations, blockage of the SCR, errors in the determine of exhaust flow by the controller, and preventing the controller to run other diagnostic tests based upon such faulty inputs.

FIG. 3 is a schematic flow chart representation of one method 124 to diagnose exhaust system malfunctions according to one non limiting embodiment of the present invention.

Specifically, step 126 is determining the ambient barometric pressure. This may be accomplished by means of an atmospheric pressure sensor that is electronically connected to an electronic controller. The location of this pressure sensor is not fixed, and may be located at the outlet of the exhaust system, or it may be located elsewhere. It is understood by those skilled in the art that the barometric pressure at the outlet of the SCR is generally accepted to be close to or the same as ambient barometric pressure.

Step 128 is determining a baseline curve of exhaust flow through the exhaust system. In one non limiting embodiment, this may be accomplished by determining the pressure change across the SCR and comparing the difference in exhaust flow rate pressure at the SCR inlet to the ambient pressure. A baseline of exhaust flow rate, which may be a predetermined value stored in memory, is compared to the change in pressure across the SCR to arrive at the baseline curve of exhaust flow through the exhaust system.

Step 130 is monitoring for changes in the baseline curve during time to diagnose an exhaust system malfunction.

While several aspects of the invention have been described, those skilled in the art recognize that the words used herein are words of description, not words of limitation. Many variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the invention as set forth in the appended claims. 

1. A method to diagnose exhaust system malfunction in an electronically controlled internal combustion engine having an exhaust system and including a Selective Catalyst Reducer (SCR) with an inlet and an outlet, comprising: determining ambient barometric pressure; determining a baseline curve of exhaust flow; monitoring said exhaust flow rate for changes in exhaust flow rate compared to change of exhaust pressure across said SCR to diagnose exhaust system malfunction.
 2. The method of claim 1, wherein said baseline exhaust flow rate is determined by determining exhaust flow rate pressure at said SCR inlet and determining a baseline of exhaust flow rate versus change of pressure across the SCR.
 3. The method of claim 1, wherein said baseline curve of exhaust flow is determined at a first operating engine cycle and stored in memory for use during said engine life.
 4. The method of claim 1, wherein said baseline curve of exhaust flow is a predetermined value stored in memory in said electronic controller.
 5. The method of claim 1, wherein a shift of the baseline curve of exhaust flow rate versus change of pressure across the SCR over time is indicative of at least one of an exhaust leak, exhaust flow rate sensor malfunction, exhaust pressure sensor malfunction, or error in engine calculated exhaust flow.
 6. The method of claim 1, wherein determination of engine airflow rate is made based upon said baseline curve of exhaust flow.
 7. The method of claim 1, wherein each exhaust system failure is stored in said electronic controller memory.
 8. The method of claim 1, wherein said exhaust system further includes a diesel particulate filter (DPF) having an inlet and an outlet, said DPF outlet in fluid communication with said SCR inlet; said SCR inlet having a pressure sensor to generate data signals to said electronic controller indicative of exhaust flow pressure at said SCR inlet.
 9. The method of claim 1, wherein said barometric pressure is the pressure of the exhaust flow at the SCR outlet.
 10. The method of claim 1, wherein said change of pressure is determined by comparing the exhaust flow pressure at said SCR inlet to the ambient barometric pressure.
 11. A computer recordable medium configured to determine exhaust system malfunction in an electronically controlled internal combustion engine having an exhaust system and including a Selective Catalyst Reducer (SCR) with an inlet and an outlet, comprising: determining ambient barometric pressure; determining a baseline curve of exhaust flow; monitoring said exhaust flow rate for changes in exhaust flow rate compared to change of exhaust pressure across said SCR to diagnose exhaust system failure. 